Since NBC sportscaster Bob Costas commented on the murder-suicide involving NFL player Jovan Belcher during Sunday Night Football, he has received a torrent of criticism from conservatives in media and the National Rifle Association. On the December 5 edition of TheO'Reilly Factor, Costas called for all gun sales to be conducted with a background check, a proposal that host Bill O'Reilly, the American public, and even NRA members largely support.

Costas drew the ire of right-wing media after favorably quoting a FoxSports.com column that noted, "If Jovan Belcher didn't possess a gun, he and [his victim] Kasandra Perkins would both be alive today." The National Rifle Association accused Costas of being involved in a "media conglomerate" conspiracy to ban all firearms. Although Costas did not mention any specific gun violence prevention proposals in his commentary, Fox News accused Costas of "lecturing America on gun control." Fox Nation and the Drudge Report claimed that Costas went on a "gun control rant."

Now Costas has gotten specific, and his proposal - to conduct background checks on all gun sales - is wildly popular.

Federal law requires individuals "engaged in the business of selling firearms" to obtain a license and perform background checks on their customers. People who say they are not "engaged in the business" may legally sell firearms without conducting a background check on purchasers. However, due to a vague definition about what activity requires a gun seller to become licensed, the private sales market has flourished. As Costas noted, an estimated 40 percent of gun sales are conducted by private sellers without a background check.

Although the NRA has downplayed this dangerous loophole, it has been exploited by killers. On October 21, a man prohibited under federal law from buying a firearm was able to purchase a gun in the private sales market - the same gun he used a day later to kill his estranged wife and two others. Even Al Qaeda has taken note, urging terrorists to use gun shows to obtain weapons without undergoing a background check.

A strong majority of the public supports closing this loophole. A January 2011 American ViewPoint/Momentum Analysis poll found that 86 percent of Americans favor requiring a background check for every gun purchase. Although the NRA opposes universal background checks, its members largely disagree. Nearly three-quarters of NRA members expressed support for background checks on anyone purchasing a gun, according to a July 2012 survey conducted by GOP pollster Frank Luntz.

From the December 5 edition of The O'Reilly Factor:

COSTAS: Roughly 40 percent of the guns purchased in this country do not require a background check for purchase.

O'REILLY: Ok. So you want a background check, right?

COSTAS: You have that. You've talked about stricter penalties, harsher penalties for those --

O'REILLY: For criminals.

COSTAS: Exactly.

O'REILLY: Right.

COSTAS: There is that. There ought to be training programs for those who purchase guns. I don't see any reason why someone should be able to purchase military-style artillery and body armor and automatic weapons. Only the police or the military should have that --